Systemic fungal diseases (systemic mycoses) are generally chronic, very slowly induced by opportunistic causative fungi which may not normally be pathogenic but represent a major threat to susceptible patients. Susceptible individuals are those with primary (inherent) immunodeficiencies, those hospitalised or living long term with indwelling surgical devices (e.g. catheters, Hickman and central lines), those undergoing invasive surgical techniques and those with secondary immunodeficiencies as a result of HIV infection, immunoablative chemotherapy or ionising irradiation, corticosteroids or other immunosuppressive drugs, prolonged exposure to antimicrobial agents etc.
Life threatening systemic fungal infections are those in which the pathogenic organisms of the blood stream, lungs and other mucosal tissue, the liver and immune sites such as the lymph glands and spleen. The diagnosis of specific fungal diseases may be made by isolation of the causative fungus from sputum, urine, blood, or the bone marrow, or with prevalent fungus types by evidence of tissue invasion. Superficial fungal infections are generally caused by dermatophytes that involve the outer layers of the skin, hair or nails. The infections may result in a mild inflammation, and cause intermittent remissions and exacerbations of a gradually extending, scaling, raised lesion. Yeasts and moulds do not generally give rise to systemic infections in healthy individuals only in immunocompromised individuals, however healthy individuals can suffer from superficial infections. Yeast infections including oral candidiasis (oral thrush) are usually restricted to the skin, and mucous membranes although yeast infections can also be systemic. Commonly, infections appear as erythematous, often itchy, exudative patches in the axillas, umbilicus, groin, between toes, and on finger-webs. Oral thrush involves an inflamed tongue, or buccal mucosa and presents as white patches of exudate, while chronic mucocutaneous candidiasis is characterized by red, pustular, crusted, thickened lesions on the forehead or nose. C. albicans can cause superficial infections of the vaginal cavity of healthy individuals; indeed up to three quarters of all women will suffer at least one episode of vaginal thrush during their lifetime. Most of these women experience infrequent attacks and respond well to drug therapy, however in some the infection is recurrent or persistent and does not respond to drug therapy.
The treatment options for infections contributed to or caused by fungi (including yeast) are severely limited and there is an urgent need to discover new therapies which inhibit or kill such organisms.
In our co-pending application, WO 2006/018652, we describe the identification of peptides that can be used to treat microbial infections in particular dermatophytic infections such as onychomycosis. For the peptides described therein, antimicrobial activity was generally confined to large cationic peptides comprising from 28 up to 200 or more basic amino acids.